Nitrocubanes

ABSTRACT

An efficient direct functionalization of nitrocubanes has been achieved by irradiation of a solution in an oxalyl halide to yield halogenated and halocarbonylated derivatives of nitrocubanes.

GOVERNMENTAL INTEREST

The Government has rights in this invention pursuant to Contract No.DAAA21-89-C-0013 awarded by the U.S. Army.

The invention described herein was made under a contract with theGovernment and may be used and licensed by or for the Government.

FIELD OF USE

This invention describes the direct functionalization of nitrocubanesvia irradiation in the presence of an oxalyl halide.

BACKGROUND OF THE INVENTION

Considerable effort in recent years has been directed toward thesynthesis of polynitrocubanes because of the potential use of this classof energetic materials as explosives, propellants, fuels and binders(Chemistry of Energetic Materials; Ed., G. A. Olah; D. R. Squire;Academic Press, Inc., San Diego, Cal., 1991. Also see Carbocyclic CageCompounds; Ed., E. J. Osawa; O. Yonemitsu; VCH Publishers, Inc., NewYork, N.Y. 1992). The compact structures of cage molecules result inhigh densities, and the introduction of NO₂ groups further enhances thedensity. The strain energy present in the cubane skeleton (>166kcal/mol) is an added bonus to its performance. Furthermore, preliminaryresults with polynitrocubanes indicate that such compounds are thermallyvery stable and are also very insensitive energetic materials.Consequently, it is of interest to introduce functional groups on thecubane skeleton which can be converted to nitro group or other activefunctionalities.

Direct functionalization of nitrocubanes, while an attractive approach,has not heretofore been realized. Cationic or anionic reactions, due tothe activity of the nitro groups give either decomposed products orrecovered starting materials. We report here an efficient directionfunctionalization of a nitrocubanes molecule by its irradiation in asolution of oxalyl halide (for a related case see Wiberg, K. B.; 10^(th)Annual Working Group Meeting, Jun. 3-6, 1992, Kiamesha Lake, N.Y. Formuch simpler cases see Wiberg, K. G.; Williams, Jr., V. Z.; J. Org.Chem., 1970, 35, 369; Appliquist, D. E.; Saski, T.; J. Org. Chem.; 1978,43, 2399). This new and potentially powerful synthetic development willgreatly shorten the number of steps necessary to obtain nitrocubanederivatives which are otherwise difficult to synthesize.

SUMMARY OF THE INVENTION

A solution of 1,4-dinitrocubane (Eaton, P. E.; et al; J. Org. Chem.;1984, 49, 185; Eaton, P. E.; Wicks, G. E.; J. Org. Chem.; 1988, 53,5353) in oxalyl chloride was irradiated under a sunlamp for 12 h at roomtemperature. After removing oxalyl chloride under reduced pressure, thereaction mixture was hydrolyzed and partioned between ethyl acetate and5% aqueous NaOH. From the organic phase was isolated2-chloro-1,4-dinitrocubane, 3, and 2,5-dichloro-1,4-dinitrocubane, 4.After acidification of the alkaline layer with HCl and extraction withethyl acetate, 2-carboxy-1,4-dinitrocubane, 5, was obtained in 68%yield. ##STR1##

The structures of 3,4 and 5 were confirmed by NMR spectrometry.Furthermore, Compound 5 was converted to the corresponding2-carbomethoxy-1,4-dinitrocubane 6 by esterification using MeOH, and themolecular structure of 6 was confirmed by X-ray crystallographicanalysis.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following section describes specific experimental procedures usedfor the synthesis:

A mixture of 1,4-dinitrocubane, 1, (388 mg, 2.0 mmol) in oxalyl chloride(50 mL) was photolyzed under a sunlamp for 18 h at room temperature.Oxalyl chloride was removed on a rotary evaporator and the solid residuewas partioned between EtOAc (40 mL) and NaOH solution (5%, 30 mL). Afterstirring for 3 h, the organic phase was separated, washed with brine,dried over anhydrous Na₂ SO₄ and concentrated under reduced pressure.The residue was chromatographed on silica gel using hexane/CH₂ Cl₂ (1:1)to give 2-chloro-1,4-dinitrocubane 3, m.p. 145°-147° C.; ¹ H NMR(CDCl₃); δ4.84 (m, 2H); 4.71 (m, 3H); and2,5-dichloro-1,4-dinitrocubane, 4, m/p. 188°-190° C.; ¹ H NMR (CDCl₃);δ4.90 (dd, 2H); 4.78 (dd, 2H).

The alkaline layer was acidified with HCl (10%) and organic materialswere extracted with EtOAc (2×30 mL). The organic phase was washed withbrine, dried over Na₂ SO₄, and concentrated via rotary evaporator togive 400 mg or a crude product which was triturated with hexane/acetone10:1, (5.0 mL) to give 2-carboxy-1,4-dinitrocubane, 5, m.p.187°-189(Dec)° C.; ¹ H NMR (acetone -d₆); δ4.96 (m,2H); 4.74 (m,3H).

Compound 5 (100 mg, 0.4 mmol) was stirred with MeOH (20 mL) and MeSO₃ H(4 drops) at reflux overnight. The reaction mixture was concentrated andthen dissolved in ethyl acetate (20 mL). The solution was washed withaqueous Na₂ CO₃ (5%), then brine, dried over anhydrous Na₂ SO₄ andconcentrated. The residue was triturated with ether/hexane (1:1) to give2-carbomethoxy-1,4-dinitrocubane 6 m.p.=165° C.; ¹ H NMR (CDCl₃), δ4.92(M,2H); 4.62 (m, 3H), 3,80 (s, 3H).

In another experiment, the solid residue from the reaction of1,4-dinitrocubane (100 mg) and oxalyl chloride (20 mL) under a sunlamp(vide supra) was treated with methanol (20 mL) for 4h at roomtemperature. The excess methanol was evaporated and the residue wasdissolved in ethyl acetate (20 mL). The organic layer was washed with 5%aqueous Na₂ CO₃ and then brine. After drying over Na₂ SO₄ and thenconcentration, the crude produce was chromatographed on silica gel usinghexane/CH₂ Cl₂ (1:1) to give compounds 3,4, and 6.

What is claimed is:
 1. 2-chloro-1,4-dinitrocubane.
 2. A method forproducing the compound of claim 1 comprising:a) removing oxalyl chloridefrom the reaction mixture of 1,4-dinitrocubane and oxalyl chloride underreduced pressure to obtain a solid residue, b) dissolving the residue inethyl acetate, c) recovering 2-chloro-1,4-dinitrocubane by achromatography step.
 3. A method for producing the compound of claim 1comprising:a) removing oxalyl chloride from the reaction mixture of1,4-dinitrocubane and oxalyl chloride under reduced pressure to obtain asolid residue, b) dissolving the residue in a 5% NaOH solution, and c)recovering 2-carboxyl-1,4-dinitrocubane from an alkaline layer.